1. Field of the Invention
This invention relates to machine tools and more particularly to control systems for moving workpieces in relation to machine tools.
2. Prior Art
Machine tools, and particularly turret punch presses include a machine having a work station with a workpiece support table partially encompassing the work station and projecting forwardly thereof. The workpiece is supported on the table and is moved thereon with respect to the work station by a workpiece gripper mechanism which includes a carriage movable in the Y directions representing movement inwardly and outwardly with respect to the machine tool work station and in the X directions representing movement laterally of the work station.
The workpiece gripper is automatically controlled from a control center and has the capability, by movement in both the X and Y directions, to present any desired exact point of the workpiece at the work station. In order to provide for precise movement of the workpiece, the automatic control must have reference points in both the X and Y direction. Further these reference points or base lines must be correlated to the position of the workpiece in the grippers so that there is a direct correlation between positioning of the grippers with respect to the base lines and positioning of the workpiece with respect to the work station.
Previously, it has been known to provide abutment faces in both the X and Y directions whereby edges of the workpiece can be presented to the abutment faces and thereafter gripped by the grippers which are located at predetermined positions with respect to the work station. In this manner, at least two edges of the workpiece will be located at predetermined positions and the grippers will be located at predetermined positions prior to the start of machining operations.
We have found that it is also possible to set the lateral or X axis base line by first positioning the workpiece in the grippers and then moving the grippers and workpiece in the X axis until the leading edge of the workpiece abuts a stop. At this point movement of the grippers is stopped and the base line is thereafter set within the automatic controls with reference to the position of the grippers at the time of abutment of the workpiece leading edge with the stop.
While such a base line setting system is highly desirable in that a large variety of workpiece sizes can be accommodated since the base line is not set until after the workpiece has been positioned in the grippers, it is undesirable in that the moving workpiece is forced against a stationary stop. This can result in deflection of or damage to the stop, and damage to the workpiece edge. Additionally, should some failure occur and should the carriage fail to stop moving at the time of edge abutment with the stop, extensive damage can occur both to the stop and to the mechanism for controlling movement of the grippers.
It would therefore be an advance in the art to eliminate the stationary stop while preserving the ability to set the base line after gripping of the workpiece by the grippers.